A spontaneously combustible catalyst may be defined as any catalyst composition which has a tendency to self-heat or combust in the presence of air or oxygen at a temperature of 200.degree. C. or lower. Particularly many hydrocarbon processing catalysts, such as hydrotreating, hydrocracking and tail-gas treating catalysts which typically contain sulfur and reduced catalysts such as hydrogenation catalysts can be classified as spontaneously combustible catalysts. Some of the hydrocarbon processing catalysts can also be a reduced catalyst.
A hydrotreating catalyst may be defined as any catalyst composition which may be employed to catalyze the hydrogenation of hydrocarbon feedstocks, and most particularly to hydrogenate particular components of the feed stock, such as sulfur-, nitrogen- and metals-containing organo-compounds and unsaturates. A hydrocracking catalyst may be defined as any catalyst composition which may be employed to crack large and complex petroleum derived molecules to attain smaller molecules with the concomitant addition of hydrogen to the molecules. A tail gas catalyst may be defined as any catalyst which may be employed to catalyze the conversion of hazardous effluent gas streams to less harmful products, and most particularly to convert oxides of sulfur to hydrogen sulfide which can be recovered and readily converted to elemental sulfur. A reduced catalyst may be defined as any catalyst that contains a metal in the reduced state such as an olefin hydrogenation catalyst. Such metals are typically reduced with a reducing agent such as, for example, hydrogen or formic acid. The metals on these reduced catalyst may be fully reduced or partially reduced.
Catalyst compositions for hydrogenation catalysts are well known and several are commercially available. Typically, the active phase of the catalyst is base on at least one metal of group VIII, VIB, IVB, IIB or IB of the periodic table. In general, the hydrogenation catalysts contains at least one element selected from Pt, Pd, Ru, Ir, Rh, Os, Fe, Co, Ni, Cu, Mo, W, Ti Hg, Ag or Au supported usually on a support such as alumina, silica, silica-alumina and carbon. Such reduced catalysts can be classified as spontaneously combustible substances.
Catalyst compositions for hydrotreating and/or hydrocracking or tail gas treating are well known and several are commercially available. Metal oxide catalysts which come within this definition include cobalt-molybdenum, nickel-tungsten, and nickel-molybdenum supported usually on alumina, silica and silica-alumina, including zeolite, carriers. Also, other transition metal element catalysts may be employed for these purposes. In general, catalysts containing at least one element selected from V, Cr, Mn, Re, Co, Ni, Cu, Zn, Mo, W, Rh, Ru, Os, Ir, Pd, Pt, Ag, Au, Cd, Sn, Sb, Bi and Te have been disclosed as suitable for these purposes.
For maximum effectiveness the metal oxide catalysts are converted at least in part to metal sulfides. The metal oxide catalysts can be sulfided in the reactor by contact at elevated temperatures with hydrogen sulfide or a sulfur-containing oil or feed stock ("in-situ").
However, it is advantageous to the user to be supplied with metal oxide catalysts having sulfur, as an element or in the form of an organo-sulfur compound, incorporated therein. These presulfurized catalysts can be loaded into a reactor and brought up to reaction conditions in the presence of hydrogen causing the sulfur or sulfur compound to react with hydrogen and the metal oxides thereby converting them into sulfides without any additional process steps being needed. These presulfurized catalysts provide an economic advantage to the plant operator and avoid many of the hazards such as flammability and toxicity, which the plant operator encounter when using hydrogen sulfide, liquid sulfides, polysulfides and/or mercaptans to sulfide the catalysts.
Several methods of presulfurizing metal oxide catalysts are known. Hydrotreating catalysts have been presulfurized by incorporating sulfur compounds into a porous catalyst prior to hydrotreating a hydrocarbon feedstock. For example, U.S. Pat. No. 4,530,917 discloses a method of presulfurizing a hydrotreating catalyst with organic polysulfides. U.S. Pat. No. 4,177,136 discloses a method of presulfurizing a catalyst by treating the catalyst with elemental sulfur. Hydrogen is then used as a reducing agent to convert the elemental sulfur to hydrogen sulfide in situ. U.S. Pat. No. 4,089,930 discloses the pretreatment of a catalyst with elemental sulfur in the presence of hydrogen. U.S. Pat. No. 4,943,547 discloses a method of presulfurizing a hydrotreating catalyst by subliming elemental sulfur into the pores of the catalyst then heating the sulfur-catalyst mixture to a temperature above the melting point of sulfur in the presence of hydrogen. The catalyst is activated with hydrogen. PCT specification WO93/02793 discloses a method of presulfurizing a catalyst where elemental sulfur is incorporated in a porous catalyst and at the same time or subsequently treating the catalyst with a liquid olefinic hydrocarbon.
However, these ex-situ presulfurized catalysts must be transported to the user or plant operator. In transportation or shipping, these presulfurized catalysts are classified as spontaneously combustible substances which are further classified into two sub-groups of material, pyrophoric substances or self-heating substances. Both groups have the same basic properties of self-heating which may lead to spontaneous combustion, but differ in the degree of spontaneous combustion. Pyrophoric substances ignite, even in small quantities, within five minutes of coming into contact with air whereas self-heating substances ignite in air only when in large quantities and after long periods of time. Pyrophoric substances are typically classified as Division 4.2 Packing Group I and self-heating substances are classified in either Packing Group II or Packing Group III according to the test procedures recommended in the Dangerous Goods Special Bulletin, April 1987, published by TDG Ottawa, Transport Canada for Class 4, Division 4.2. These spontaneously combustible substances must be packaged in an United Nations (UN) designated 250 kg metal drum or in a smaller package of 100 kg plastic fiber drum or even smaller.
It is desirable to transport these presulfurized catalysts in larger quantities such as in flow bins or super sacks for economic reasons and ease of handling. But, in order to transport such catalysts in such larger quantities safely, they must pass the test for spontaneously combustible substances.
Further, some of the prior art ex-situ methods of presulfurizing supported metal oxide catalysts have suffered from excessive stripping of sulfur upon start-up of a hydrotreating reactor in the presence of a hydrocarbon feedstock. As a result of sulfur stripping, a decrease in catalyst activity or stability is observed. Further, the stripping of sulfur can cause fouling of downstream equipment.
Therefore, it is an object of the present invention to treat spontaneously combustible catalysts in a manner to suppress the self-heating properties of the catalysts. It is another object of the present invention to prepare an air and/or oxygen stable, presulfurized or presulfided catalyst, either fresh or regenerated with minimal stripping of sulfur and/or decrease in catalyst activity.